1. Field of the Invention
The present invention relates to a method for monitoring yarn tension in a yarn manufacturing process while the yarn spun by a spinning device is wound by a winding device.
2. Description of the Related Art
Recently, in a yarn manufacturing process for manufacturing a synthetic fiber yarn such as polyamide or polyester, a yarn spun by a spinning device is wound by a winding device including a traverse mechanism, a spindle for attaching a bobbin thereto, a contact roller adapted to contact the yarn wound around the bobbin to apply a surface pressure to the yarn, and a winding condition detecting means. A tension of the yarn is always detected by a yarn tension detecting means arranged on the upstream side of the winding device, to monitor the yarn manufacturing process and to detect whether the manufacturing process is in a normal condition or not, by analyzing the detected tension.
The yarn tension detected by the yarn tension detecting means varies due to several factors. The variation in the yarn tension is caused, on one hand, by a real abnormality in the yarn manufacturing process and, on the other hand, by the production factors. One of the tension variations due to the production factors is based on a change in a manufacturing condition such as a change in a traverse speed and a change in a rotational speed of the spindle.
The yarn is wound by the winding device under one of several different traversing methods. For example, the random traversing method, the ribbon jump traversing method, the programmed traversing method, the multi-wind traversing method, and the combination of these traversing methods are known. For example, FIG. 3 shows the random traversing method in which the traverse speed is cyclically changed to effect ribbon break while the traversing angle is maintained constant. FIG. 4 shows the ribbon jump traversing method in which the traverse speed is suddenly changed at ribbon regions only while the traversing angle is maintained constant. FIG. 5 shows the programmed traversing method in which the traverse speed is always changed from the start of the winding to the end of the winding to change traversing angles. FIG. 6 shows the multi-wind traversing method in which the traverse speed is changed to change the winding ratio at every ribbon region. The traverse speed largely varies in these cases.
In addition, in the winding speed changing winding, the rotational speed of the spindle varies from the start of the winding to the end of the winding, as shown in FIG. 7.
If the traverse speed varies, the yarn tension varies in proportion to the change of the traverse speed, as shown in FIGS. 3 to 6, and the yarn tension may be out of an abnormal judging reference having a predetermined range, so that the yarn manufacturing process may be judged to be in an abnormal condition and the abnormal signal is thus outputted.
In addition, if the winding speed varies, the yarn tension varies in proportion to the winding speed, as shown in FIG. 7, so that the variation of the yarn tension from the start of the winding to the end of the winding becomes larger and exceeds the allowed abnormal judging reference range in the yarn winding operation, so that the yarn manufacturing process is judged to be in an abnormal condition when the detected tension is out of the abnormal judging reference range and the abnormal signal is thus outputted.
In this way, there is a case where the abnormal signal is outputted even though the winding condition is normal, and it is difficult to distinguish the variation of the yarn tension due to a real abnormality in the yarn manufacturing process from the variation of the yarn tension inevitably arising depending on the manufacturing conditions.
In order to avoid the output of the abnormal signal due to a variation of the yarn tension arising from the manufacturing conditions, it is necessary to broaden the range between the upper limit and the lower limit of the abnormal judging reference. However, there is a problem in that a real abnormality which produces only a small change in the tension, such as a change in the amount of oil attached to the yarn, filament break, and a change in the polymer viscosity, is not always detected.